Position compensating differential locking mechanism

ABSTRACT

A differential with an improved locking mechanism is provided. The differential includes first and second clutch members in the form of a differential case having a first set of teeth and a an axle shaft mounted clutch collar having a second set of teeth. A yoke urges the clutch into an out of engagement and is supported on a pivot shaft. The yoke is selectively urged in one direction by an actuator acting on a lever on the pivot shaft. The lever is coupled to the yoke by a spring. The yoke is urged in an opposite direction by one or more return springs mounted on the same pivot shaft. The compact nature of the locking mechanism and the balance of forces provided by the springs and actuator provide an inexpensive and reliable locking mechanism.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a differential, and more particularly,to a position compensating differential locking mechanism.

2. Discussion of Related Art

Differential gear mechanisms, simply referred to as differentials, arewell known devices frequently used in the drive trains of most vehicles.The differential is usually connected between an input driving shaft{typically a drive shaft from the vehicle engine} and a pair of outputdriven shafts (typically a pair of axle shafts connected to the vehiclewheels). The differential distributes torque from the input shaftequally to the two output shafts, while permitting such output shafts torotate at different speeds under certain conditions. As a result, torqueis supplied to both wheels of the vehicle as it negotiates a turn, whilepermitting the outside wheel to turn faster than the inside wheel.

In a conventional open differential, the movements of the variousinternal components of the differential are not restricted in anysignificant fashion. Thus, the differential functions in the desirablemanner described above under most circumstances. However, when one ofthe wheels loses traction with the ground, due to, for example, wet oricy surfaces, the differential will reduce the amount of torque suppliedto the other wheel. Consequently, the vehicle can become immobilized.

To prevent immobilization, some differentials are provided with alocking mechanism. When actuated, the locking mechanism restricts themovement of some of the differential's internal components. Thisrestriction allows the drive shaft to provide torque to both wheelsinstead of providing torque only to the wheel with less traction. Somedifferential locks remain locked and automatically unlock while turningcorners. Other differentials use a driver-initiated control to manuallyengage and disengage the lock at the driver's command.

One conventional differential locking mechanism includes a first set ofteeth on a differential case of the differential and a clutch collarhaving a second set of teeth configured to selectively engage the firstset of teeth. The clutch collar is supported on a drive axle shaftextending through the differential case. The mechanism further includesa yoke supported on a pivot shaft and received within a groove in theclutch collar. A lever is also supported on the pivot shaft and isdisposed outside of the differential housing where it may be coupled toa spring-loaded cable system manually operated by the vehicle operator.This conventional differential has several disadvantages. First, thelocking mechanism can only be engaged while the vehicle is at rest.Second, the manual engagement of the locking mechanism requires aphysical effort on the part of the operator. Third, the lockingmechanism requires a relatively large amount of space to link the leverand the cable system.

The inventors herein have recognized a need for a differential that willminimize and/or eliminate one or more of the above-identifieddeficiencies.

SUMMARY OF THE INVENTION

The present invention provides a differential with a positioncompensating differential locking mechanism.

A differential in accordance with one embodiment of the presentinvention includes a differential case having a first set of teeth anddefining a central bore. A drive axle shaft is disposed within thecentral bore and is rotatable therein. The differential also includes aclutch collar mounted on the drive axle shaft. The clutch collar has asecond set of teeth configured to selectively engage the first set ofteeth and to prevent relative rotation between the drive axle shaft andthe differential case. The clutch collar further defines a groove. Ayoke is supported on a pivot shaft and is received within the groove inthe clutch collar. The differential further includes a lever supportedon the pivot shaft and a first spring disposed between the yoke and thelever. An actuator selectively urges the lever and the yoke in a firstrotational direction to a first position. A second spring urges thelever and the yoke in a second rotational direction to a secondposition. The first and second sets of teeth are urged into engagementin one of the first and the second positions and the first and thesecond sets of teeth are urged to disengage in another of the first andthe second positions.

A differential in accordance with the present invention has one or moreadvantages as compared to the prior art. First, the differential canoperate freely during vehicle travel regardless of the level ofengagement between the opposed clutch members. Second, the inventivedifferential may eliminate the need for manual operation of thedifferential locking mechanism. Third, the locking mechanism of theinventive differential is compact thereby conserving vehicle space.

This and other features and objects of this invention will becomeapparent to one skilled in the art from the following detaileddescription and the accompanying drawings illustrating features of thisinvention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a differential in accordance withone embodiment of the present invention.

FIG. 2 is an exploded view of a portion of the differential of FIG. 1.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring now to the drawings wherein like reference numerals are usedto identify identical components in the various views, FIG. 1illustrates a cross-sectional view of a differential 10 in accordancewith one embodiment of the present invention. Differential 10 isprovided to enable two wheels (not shown) in a vehicle that are disposedabout a common rotational axis to rotate at different speeds.Differential 10 may include several conventional components known tothose of skill in the art. In particular, differential 10 may include ahousing 12 composed of multiple members and a pinion shaft 14 thatextends through an opening in housing 12 and supports a pinion gear 16.The pinion shaft 14 may be supported for rotation within housing 12 bybearings 18, 20 and may be driven by a power input shaft (not shown).Differential 10 may further include a ring gear 22 coupled to orintegral with a differential case 24 and driven by pinion gear 16. Case24 is supported within housing 12 by bearings 26, 28 and may house aspider 30 on which one or more differential gears 32, 34 are mounted.Gears 32, 34 mesh with side gears 36, 38 splined to drive axle shafts40, 42 that are disposed in central bores 44, 46, respectively, definedin case 24. Shafts 40, 42 are rotatable within bores 44, 46 about anaxis 48. In accordance with the present invention, differential 10 mayalso include a differential locking mechanism 50.

Referring to FIGS. 1 and 2, mechanism 50 is provided to selectively lockand unlock differential 10 to prevent relative rotation between shafts40, 42. Mechanism 50 may include a clutch collar 52, a yoke 54, a pivotshaft 56, a lever 58, an actuator spring 60, an actuator 62, and one ormore return springs 64, 66.

Clutch collar 52 comprises one member of a clutch used to lockdifferential 10 and thereby prevent relative rotation between shaft 40and case 24. Collar 52 defines a bore 68 configured to receive shaft 40.Collar 52 is mounted on shaft 40 and is axially movable on shaft 40through, for example, splines disposed on a radially outer surface ofshaft 24 and a radially inner surface of collar 52. Collar 52 mayinclude a set of teeth 70 at one axial end of collar 52 configured toselectively engage another set of teeth 72 on one axial end of case 24.Teeth 70 on collar 52 may be machined with a negative one-degree draftto aid in retaining engagement between teeth 70, 72 during rotation.Collar 52 also defines a peripheral, circumferentially extending groove74 proximate another axial end of collar 52.

Yoke 54 is provided to move collar 52 axially inboard and outboard andto thereby move teeth 70 on collar 52 into and out of engagement withteeth 72 on case 24. Referring to FIG. 2, yoke 54 includes asubstantially U-shaped member 76 configured to be received within groove74 of collar 52. Yoke 54 may further include a substantially U-shapedbracket 78 coupled to member 76 through welds or other conventionalfasteners. Bracket 78 opens in an opposite direction as compared tomember 76 and includes aligned apertures 80, 82 proximate each endenabling yoke 54 to be supported on pivot shaft 56.

Pivot shaft 56 enables pivoting motion of yoke 54 and lever 58. Shaft 56is supported at either longitudinal end within one or more bores 84, 86in housing 12 as shown in FIG. 2. Bushings (not shown) may be interposedbetween the inner surface of housing 12 defining bores 84, 86 and shaft56. Shaft 56 extends through apertures 80, 82 in bracket 78 of yoke 54.

Lever 58 is provided for use in causing rotation of yoke 54 about pivotshaft 56. Lever 58 includes an aperture 86 through which shaft 56extends to support lever 58. Lever 58 is free to rotate about shaft 56and is disposed between the opposed ends of bracket 78. Lever 58 furtherdefines a groove 88 configured to receive a portion of spring 60.

Spring 60 couples yoke 54 and lever 58 and is disposed between yoke 54and lever 58. Spring 60 may comprise a double coil spring wherein thecoils are sized to receive pivot shaft 56. Spring 60 includes two tangs90, 92 that are coupled to yoke 54 and spring 60 is received within theopposed ends of bracket 78.

Actuator 62 is provided to selectively urge lever 58 and yoke 54 in onerotational direction (clockwise in the illustrated embodiment) to one oftwo positions. In the illustrated embodiment, yoke 54 is moved to aposition that results in disengagement of teeth 70, 72 from one another.It should be understood, however, that actuator 62 could alternativelyurge yoke 54 in the opposite rotational direction to another positionthat results in engagement of teeth 70, 72. In a preferred embodiment ofthe invention, actuator 62 comprises an electronic actuator and, inparticular, a push-type solenoid. It should be understood, however, thatactuator 62 may take on a variety of forms including, for example, amagnetic latch type solenoid. Actuator 62 includes a plunger 94 that isselectively urged outwardly from actuator 62 to engage lever 58 andcause rotation of yoke 54.

Return springs 64, 66 are provided to urge yoke 54 in another rotationaldirection (counterclockwise in the illustrated embodiment), opposite tothe rotational direction urged by actuator 62, and to another position.In the illustrated embodiment, this position results in engagement ofteeth 70, 72. It again should be understood, however, that returnsprings 64, 66 could alternatively urge yoke 54 in the oppositedirection to a position resulting in disengagement of teeth 70, 72.Return springs 64, 66 include a coil sized to receive pivot shaft 56 andare located on pivot shaft 56 on either side of bracket 78 of yoke 54.Springs 64, 66 are coupled to yoke 54 at one end and at housing 12 atanother end. Although two return springs 64, 66 are shown in theillustrated embodiment, it should be understood that varying numbers ofsprings could be used without departing from the spirit of the presentinvention.

Referring again to FIGS. 1 and 2, in the illustrated embodiment returnsprings 64, 66 normally urge yoke 54 in a first rotational directioncausing axial movement of collar 52 in an inboard direction towards case24 and engagement of teeth 70, 72. In one constructed embodiment,springs 64, 66 exert about 1.5 lbs. of force. Disengagement of teeth 70,72 is accomplished by energizing actuator 62 using a control signal (notshown) generated by the vehicle operator or a programmablemicrocontroller (not shown). In one constructed embodiment, the plunger94 of actuator 62 initially is driven by 12 V_(DC). This current causesplunger 94 to move approximately 0.220 inches and plunger 94 exerts aninitial force of about 10 lbs. at the start and 13.5 lbs. once fullyextended. After extension, 3 V_(DC) is used to maintain plunger 94 inplace and a holding force of about 9 lbs is exerted by plunger 94.Extension of plunger 94 causes rotation of lever 58 about shaft 56.Because teeth 70, 72 remained engaged under the torque of axle shaft 40,rotation of lever 58 compresses spring 60 creating a torsional load orspring force of about 7.5 lbs acting against yoke 54 in one constructedembodiment. Upon a reduction in torque in axle shaft 40, spring 60forces yoke 54 to rotate in a clockwise direction to a position in whichteeth 70, 72 become disengaged. One advantage of the present inventionis that the compression of spring 60 by the initial rotation of lever 58in response to plunger 94 creates a secondary force urging yoke 54 awayfrom lever 58 thereby reducing the force required from actuator 62. Asyoke 54 pivots, the tension in spring 60 decreases while the tension inreturn springs 64, 66 increases until the opposing forces are balanced.The use of springs 60 and 64, 66 in the present invention isadvantageous because springs 60 and 64, 66 allow independent adjustmentof the forces urging yoke 54 in either rotational direction and,consequently, clutch collar 52 in either axial direction. For example,selecting the balance of these spring forces determines the extent towhich clutch collar 52 will move axially outboard from case 24 upondisengagement.

Upon deenergization of actuator 62, or a failure in the power source foractuator 62, return springs 64, 66 urge yoke to a position in whichteeth 70 of clutch collar 52 and teeth 72 of case 24 become engaged.Movement of yoke 54 also causes corresponding movement of lever 58through spring 60 thereby urging plunger 94 into a retracted position inactuator 62. In the embodiment shown in FIG. 1, springs 64, 66 urge yoke54 to rotate in a counterclockwise direction thereby causing collar 52to move axially in an inboard direction.

A differential in accordance with the present invention represents animprovement over prior art differentials. The inventive differential canoperate freely during vehicle travel regardless of the level ofengagement between the teeth 70, 72 on the clutch collar 52 anddifferential case 24. The inventive differential may also eliminate theneed for manual operation of the differential locking mechanism throughuse of an electronically controlled actuator 62. The locking mechanismof the inventive differential is also compact with lever 58 disposedinside the differential housing 12 thereby conserving vehicle space.

While the invention has been particularly shown and described withreference to the preferred embodiment thereof, it is well known by thoseskilled in the art that various changes and modifications can be made inthe invention without departing from the spirit and scope of theinvention as defined by the following claims.

We claim:
 1. A differential comprising: a differential case having a first set of teeth and defining a central bore; a drive axle shaft disposed within said central bore and rotatable therein; a clutch collar mounted on said drive axle shaft, said clutch collar having a second set of teeth configured to selectively engage said first set of teeth and to prevent relative rotation between said drive axle shaft and said differential case, said clutch collar further defining a groove; a yoke supported on a pivot shaft and received within said groove in said clutch collar; a lever supported on said pivot shaft; a first spring disposed between said yoke and said lever; an actuator that selectively urges said lever and said yoke in a first rotational direction to a first position; and a second spring that urges said lever and said yoke in a second rotational direction to a second position; wherein said first and said second sets of teeth are urged into engagement in one of said first and said second positions and said first and said second sets of teeth are urged to disengage in another of said first and said second positions.
 2. The differential of claim 1 wherein urging said lever in said first rotational direction compresses said first spring, said first spring exerting a spring force urging said yoke in said first rotational direction.
 3. The differential of claim 2 wherein said first spring remains compressed and said first and said second set of teeth remain engaged until said drive axle shaft experiences a reduction in torque.
 4. The differential of claim 1 wherein said actuator exerts an initial force on said lever, said initial force followed by a holding force, said holding force being less than said initial force.
 5. The differential of claim 1 wherein said actuator comprises an electronic actuator.
 6. The differential of claim 1 wherein said actuator comprises a solenoid.
 7. The differential of claim 1 wherein said second set of teeth have a negative one-degree draft.
 8. The differential of claim 1 wherein said first spring is a double coil spring.
 9. A differential comprising: a differential case having a first set of teeth and defining a central bore; a drive axle shaft disposed within said central bore and rotatable therein; a clutch collar mounted on said drive axle shaft, said clutch collar having a second set of teeth configured to selectively engage said first set of teeth and to prevent relative rotation between said drive axle shaft and said differential case, said clutch collar further defining a groove; a yoke supported on a pivot shaft and received within said groove in said clutch collar; a lever supported on said pivot shaft; a first spring disposed between said yoke and said lever; an actuator that selectively urges said lever and said yoke in a first rotational direction to a first position, said first position being achieved when said first set of teeth are disengaged from said second set of teeth; and a second spring that urges said lever and said yoke in a second rotational direction to a second position, said second position being achieved when said first set of teeth are engaged with said second set of teeth.
 10. The differential of claim 9 wherein said first spring remains compressed and said first and said second set of teeth remain engaged until said drive axle shaft experiences a reduction in torque.
 11. The differential of claim 9 wherein said actuator exerts an initial force on said lever, said initial force followed by a holding force, said holding force being less than said initial force.
 12. The differential of claim 9 wherein said actuator comprises an electronic actuator.
 13. The differential of claim 9 wherein said actuator comprises a solenoid.
 14. The differential of claim 9 wherein said second set of teeth have a negative one-degree draft.
 15. The differential of claim 9 wherein said first spring is a double coil spring.
 16. A differential comprising: a differential case having a first set of teeth and defining a central bore; a drive axle shaft disposed within said central bore and rotatable therein; a clutch collar mounted on said drive axle shaft, said clutch collar having a second set of teeth configured to selectively engage said first set of teeth and to prevent relative rotation between said drive axle shaft and said differential case, said clutch collar further defining a groove; a yoke supported on a pivot shaft and received within said groove in said clutch collar; a lever supported on said pivot shaft; a double coil spring disposed between said yoke and said lever; a solenoid that selectively urges said lever and said yoke in a first rotational direction to a first position upon energization, said first position being achieved when said first set of teeth are disengaged from said second set of teeth; and at least one return spring that urges said lever and said yoke in a second rotational direction to a second position, said second position being achieved when said first set of teeth are engaged with said second set of teeth.
 17. The differential of claim 16 wherein said double coil spring remains compressed and said first and said second set of teeth remain engaged until said drive axle shaft experiences a reduction in torque.
 18. The differential of claim 16 wherein said solenoid exerts an initial force on said lever, said initial force followed by a holding force, said holding force being less than said initial force.
 19. The differential of claim 16 wherein said second set of teeth have a negative one-degree draft.
 20. The differential of claim 6 wherein said solenoid comprises a single-acting solenoid.
 21. The differential of claim 20 wherein said single-acting solenoid comprises a push-type solenoid.
 22. The differential of claim 20 wherein said single-acting solenoid comprises a magnetic latching solenoid. 